When manufacturing rotatable memory media, such as optical, magnetic, magnetooptical or holographic memory media, there is a need for making a groove in a surface with great accuracy. The grooves may have a width in the order of 1-100 nanometers.
A method known for this purpose is referred to as lithography, in which a substrate is exposed to a lithographic beam, for instance a particle beam, such as an ion beam or an electron beam. Such a beam can be very small in cross-section. When such a lithographic beam falls on the surface of the substrate, a point of exposure is formed, whose area essentially corresponds to the cross-section of the lithographic beam.
This type of lithography can be used for making a relief pattern for a stamp for imprint lithography, which is described in more detail, for instance, in WO01/42858A1 and WO01/69317, which are incorporated herewith by reference.
This technology may become interesting in the manufacture of the new generation hard disks, where the surface is provided with a structure for high storage capacity. In order to increase the storage capacity, it is desirable to decrease the size of the areas to be magnetized. There is, however, a limit to how far it is possible to force the reduction of the areas before an area is affected by neighboring areas to such an extent that storage of data in an area changes data in a neighboring area.
One way of coping with this is to define in advance magnetizable areas in each of the layers, which areas are separated. For instance such magnetizable areas can take the form of concentric rings, hereinafter referred to as “grooves”, which are distributed over the surface of a rotatable disk.
When manufacturing relief patterns for imprint lithography of substrates which are to obtain such grooves, it is desirable to provide a stamp in the same format as the intended product, the stamp having a large number of concentric grooves, where each groove has as small radial variations as possible.
A problem in connection with the making of such concentric grooves involves tolerance variations in the groove made by the lithographic beam, which are caused by mechanical slack or play that arises in the equipment used and that is uncontrollable per se and difficult to handle. This problem occurs especially in conjunction with very small structures being made with great accuracy on a relatively large surface. To make such structures, use is preferably made of particle beams, such as electron or ion beams, since electromagnetic radiation, in case of e.g. optical wavelengths or X-ray wavelengths, usually cannot be focused to the same small dimensions.
U.S. Pat. No. 5,621,216 discloses a method of handling position errors at spot boundaries when manufacturing X-ray masks for E-beam lithography. This is done by the electron beam resist being partially exposed during a plurality of exposures, whereby an average exposure is achieved. The technology suggested in U.S. Pat. No. 5,621,216 is, however, only suited for exposure of small surfaces since the electron beam can only be controlled over a very small area.
There is thus a need for a method for making, by means of a lithographic beam, concentric grooves in a surface layer, by which method the influence exerted by mechanical slack or play of the above type is reduced.